Polyurethane stator for a progressive cavity pump

ABSTRACT

A progressive cavity pump including a shell, a stator removably affixed within the shell, a rotor positioned interior of the stator within the shell and a motor interconnected to the rotor so as to rotate the rotor. The stator is formed of polyurethane material. The polyurethane material of the stator has a durometer hardness of 50-98 shore. The polyurethane material of the stator has an operating temperature of between 212° F. and 400° F. The polyurethane material of the stator had a tensile stress of between 100-5100 p.s.i. The stator is positioned between the fluid inlet and outlet of the shell.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to progressive cavity pumps. More particularly, the present invention relates to the configuration of stators which are positioned over the rotor of the progressive cavity pump. The present invention also relates to mud pumps, as used in directional drilling.

[0003] 2. Description of Related Art

[0004] Progressive cavity pumps have been known since their invention was disclosed in U.S. Pat. No. 1,892,217, entitled “Gear Mechanism” to Moineau. The helicoidal rotor and the stator engage with each other along a sealing line to create cavities which progress axially as the rotor is rotated relative to the stator. Because of the required sealing and sliding contact concept of a Moineau pump, the stator and the rotor become subject to extensive wear, which necessitates frequent replacement of the stator and/or the rotor. Commercially available Moineau pumps, as well as those described in the prior art, require extensive disassembly of the pumping apparatus to replace the worn stator and/or rotor, in addition to the downtime loss of use. In a pump device, rotary motion is applied to the rotor which causes fluids and solids to be passed therethrough. Where the progressive cavity device is used as a motor, one method is to apply fluid pressure to the cavity to cause the rotor to rotate, the power therefrom having many uses. In the case of use in drilling wells, the ability to decrease the frequency of downtime and extend the useful life of the motor is a desired objective.

[0005] The conventional Moineau pump and motor have used a rubber or elastomer material bonded to steel for the stator contact surface. Such elastomers include not only natural rubber, but also synthetics, such as G.R.S. neoprene, butyl and nitrile rubbers, although there are other types such as soft P.V.E. The key, of course, is to make the elastomer properly soft enough to maintain the sealed cavity, yet hard enough to withstand the abrasive wear from the working contact between the rotor and the stator. The rotor is usually made of steel.

[0006] Rubber, when used as the stator contact surface, is not preferable in high temperature environments because of its low heat conductivity. In addition, as progressive cavity devices increase in diameter and/or length, the flow characteristics to maintain a successful and long-lasting bond of the rubber to the steel housing becomes more difficult. Also, where hydrocarbons make up the material to be pumped, such as in oil producing wells, rubber is known to deteriorate.

[0007] The construction of the stator of the progressive cavity pump is a particular problem where highly abrasive material is required to be pumped. In certain circumstances, wastewater sludge must be pumped through the progressive cavity pump. Because of the high solids content of such sewage sludge, the stator can easily wear and require immediate replacement. Where conventional progressive cavity pumps are used having stators using buna-N and EPDM stators, the life of the stators is one week or less at maximum capacity. As such, a need has developed so as to create a stator having a long life.

[0008] It is an object of the present invention to provide a stator for a progressive cavity pump having excellent wear resistance.

[0009] It is another object of the present invention to provide a stator for a progressive cavity pump that is able to withstand greatly elevated temperatures.

[0010] It is a further object of the present invention to provide a stator for a progressive cavity pump that can withstand high pressures.

[0011] It is still a further object of the present invention to provide a stator for a progressive cavity pump which can be used in conjunction with the pumping of very abrasive compounds, such as sewage sludge.

[0012] It is still a further object of the present invention to provide a stator for a progressive cavity pump which has a very high tensile strength.

[0013] It is still a further object of the present invention to provide a stator for a progressive cavity pump which is relatively inexpensive, easy to produce and easy to install.

[0014] These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.

BRIEF SUMMARY OF THE INVENTION

[0015] The present invention is a progressive cavity pump comprising a shell, a stator removably affixed within the shell, a rotor positioned interior of the stator within the shell, and a motor interconnected to the rotor so as to rotate the rotor. The stator is formed of a polyurethane material.

[0016] The polyurethane material of the stator has a durometer hardness of between 50 and 98 shore. The stator has an operating temperature of between 212° F. and 400° F. The polyurethane material of the stator has a tensile strength of between 100 and 5100 p.s.i. In the preferred embodiments of the present invention, the polyurethane material of the stator is either a M-80-A-100-0600 elastomer or a M-50-d-100-1400 elastomer. The stator will have a diameter of between 2 inches and 10 inches inclusive.

[0017] In the present invention, the shell will have a cap member removably affixed at an end thereof so that the stator can be removable therethrough. The rotor will have the configuration of a helix with a pitch. The stator is a helix with a pitch that is twice the pitch of the rotor. The shell has an inlet and an outlet. The stator is positioned between the fluid inlet and fluid outlet of the shell. A drive means is connected to the motor and to the rotor so as to rotate the rotor relative to a rotation of a shaft of the motor.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0018]FIG. 1 is a partial cross-sectional view showing the progressive cavity pump using the stator in accordance with the teachings of the present invention.

[0019]FIG. 2 is a cross-sectional view showing the stator as received within the interior of the shell of the progressive cavity pump.

[0020]FIG. 3 is a graph showing the benefits of the stator of the present invention in comparison with prior art stators. The graph of FIG. 3 shows tensile stress versus percent elongation.

DETAILED DESCRIPTION OF THE INVENTION

[0021] Referring to FIG. 1, a progressive cavity pump 13 includes a rotor 5 turning within the stator 4. In a typical configuration, the rotor 5 is geometrically a large pitched helix, while the stator is a body with a two start helix with twice the pitch of a rotor. As a result, conveying spaces (cavities) are formed between the stator 4 and the rotor 5.

[0022] During pumping, these cavities are filled with product moving continuously from inlet 10 to outlet 11. As a result of the smooth transition from one cavity to the next, the pump delivery is almost pulsation free. The conveying spaces are sealed by the interference between the rotor 5 and the stator 4. The stator 4 is held within a rigid shell 15. The volume of the cavities during their advancement stays constant. The rotor 5 moves radially within the stator.

[0023] Rotor 5 is driven by way of drive shaft 6A and connecting shaft assembly 6B. Drive shaft 6A is connected to a suitable power source such as an electric, hydraulic, pneumatic or other type of motor 72. To accommodate the orbital movement of rotor 5, connecting shaft assembly 6B either comprises a shaft made of a flexible material, such as, a spring steel or comprises rigid shaft 6C provided with joints 8A and 8B at its ends, as shown in FIG. 1. Such joints may, for example, be gear, pin or universal joints.

[0024] Joints 8A and 8B are provided with seals or elastomeric boots 17 to prevent pumped material, e.g. sewage sludge, from entering the joints. Preferably, the joints are lubricated by a liquid, such as a lubricating oil. In such a case, the seals, boots or sleeves, in addition to keeping pumped material out of the joints, also keep the lubricant out of the pumped material.

[0025]FIG. 2 shows an example of the stator 4 as received within the interior of the shell 15. The rotor 5 is illustrated as positioned within the cavity 20 of the progressive cavity pump 13.

[0026] In FIG. 2, it can be seen that the stator has wing areas 21 which are slidably received within channels formed in the rigid shell 15. As such, the stator can easily be removed from the interior of the shell by disconnecting a cap affixed to the end of the shell. Alternatively, various other mechanical connection techniques can be used so as to maintain the stator within the rigid shell 15. For example, the rigid shell 15 can be a two-part shell that is hingedly connected together so that the shell 15 can be separated and the stator 4 easily removed. In another technique, mechanical fasteners can be affixed through the shell 15 so as to secure the stator 4 in its desired position.

[0027] Importantly, in the present invention, the stator 4 is formed of a polyurethane material. The prior art uses of the stator 4 have not shown the use of a polyurethane material. In particular, the polyurethane material which is used for the stator 4 has a durometer hardness of between 50 and 98 shore. The particular polyurethane material that is used for the stator has an operating temperature of between 212° F. and 400° F. The polyurethane material used for the stator 4 has a tensile strength of between 100 to 5100 p.s.i. Specifically, the polyurethane material for the stator is either a M-80-A-100-0600 elastomer or a M-50-d-100-1400 elastomer. The stator will have a diameter of between 2 inches and 10 inches, inclusive.

[0028]FIG. 3 shows a graph of tensile stress (p.s.i.) versus % elongation. The various lines A, B, C, D and E show the various material used for the stator for the present invention. A comparison between the prior art stator materials (shown by lines A, B and C) can be compared with the elastomers used for the stator for the present invention (shown by lines D and E).

[0029] Line A shows the use of neoprene at 65 shore A. It can be seen that neoprene can only withstand tensile stress of approximately 500 p.s.i. Line B represents natural rubber at 50 shore. The natural rubber, when used for the stator 4, can only withstand tensile stress of approximately 500 p.s.i. A synthetic elastomer M-50-A-100-0200 shows a maximum tensile stress of 1,000 p.s.i. as represented by line C.

[0030] The present invention in either of its preferred embodiments is shown by lines D and E. Line D represents the M-80-A-100-0600 elastomer. This elastomer, when used for the stator 4, exhibits a tensile stress of approximately 2400 p.s.i. Finally, line E represents the M-50-d-100-1400 as used for the stator 4. This material withstands a tensile stress of over 5,000 p.s.i. As can be seen in the graph of FIG. 3, the use of the polyurethane material, particularly the M-80-A-100-0600 and the M-50-d-100-1400 elastomers, exhibits significant improvements over the natural rubber and neoprene material as used on prior art stators.

[0031] These elastomers, as used in the stator 4 of the present invention, withstand temperatures of 250° F. at pressures exceeding 500 p.s.i.g. These elastomers have excellent heat resistance along with better abrasive characteristics.

[0032] In an experiment with the present invention, these elastomers were formed into an eight inch stator. The stator was put into service at the Dane County Waste Water Facility. The previous stator life was 47 hours of operation using the EPDM material. By using the elastomer of the present invention, the life of the stator was extended to over 167 hours.

[0033] These elastomers have higher oil and solvent resistance and better aging properties than general-purpose rubbers, such as Buna-N and EPDM. They have greater abrasion and tear resistance than neoprene or natural rubber, coupled with greater load-bearing capacity. Their extensibility and impact strength are greater than most plastics.

[0034] It has been found that the use of these elastomers in high wear environments, such as mud motors and progressive cavity pumps, when pumping dry lime, shows more than fourteen times the service life extension over stators of EPDM, Buna-N material and natural rubber. The M-80-A-100-0600 elastomer outlasted a stainless steel mesh by at least four hundred times the service life, at only seven times the actual cost. The stainless steel mesh screen lasted only ten days before requiring replacement.

[0035] The present invention is particularly adapted for use in pumping sewage sludge. Experiments have shown that replacement of the prior art stator with the polyurethane stator of the present invention extended pump life of the stator from one week with the prior art stators to three weeks with the present invention. By avoiding replacement of the stator, the pump can have longer operating life, require less maintenance, and save replacement costs.

[0036] The foregoing disclosure and description of the invention is illustrative and explanatory thereof. Various changes in the details of the illustrated construction may be made within the scope of the appended claims without departing from the true spirit of the invention. The present invention should only be limited by the following claims and their legal equivalents. 

We claim:
 1. A progressive cavity pump comprising: a shell; a stator removably affixed within said shell, said stator being of a polyurethane material; a rotor positioned interior of said stator within said shell; and a motor interconnected to said rotor so as to rotate said rotor.
 2. The pump of claim 1, said shell having a cap member removably affixed at an end thereof, said stator being removable therethrough.
 3. The pump of claim 1, said rotor having a configuration of a helix with a pitch, said stator being a helix with a pitch which is twice the pitch of said rotor.
 4. The pump of claim 1, said polyurethane material of said stator having a durometer hardness of 50-98 shore.
 5. The pump of claim 1, said polyurethane material of said stator having an operating temperature of between 212° F. and 400° F.
 6. The pump of claim 1, said polyurethane material of said stator having a tensile stress of between 100 and 5100 p.s.i.
 7. The pump of claim 1, said polyurethane material of said stator being a M-80-A-100-0600 elastomer.
 8. The pump of claim 1, said polyurethane material of said stator being a M-50-d-100-1400 elastomer.
 9. The pump of claim 1, said stator having a diameter between 2 inches and 10 inches inclusive.
 10. The pump of claim 1, said shell having an inlet and an outlet, said stator positioned between said inlet and said outlet.
 11. The pump of claim 1, further comprising: a drive means connected to said motor and said rotor, said drive means rotating said rotor relative to a rotation of a shaft of said motor.
 12. A stator for a progressive cavity pump comprising: a body having a helix shape, said body being of a polyurethane material.
 13. The stator of claim 12, said polyurethane material of said body having a durometer hardness of 50-98 shore.
 14. The stator of claim 12, said polyurethane material of said body having an operating temperature of between 212° F. and 400° F.
 15. The stator of claim 12, said polyurethane material of said body having a tensile stress of between 100 and 5100 p.s.i.
 16. The stator of claim 12, said polyurethane material of said body being a M-80-A-100-0600 elastomer.
 17. The stator of claim 12, said polyurethane material of said body being a M-50-d-100-1400 elastomer.
 18. The stator of claim 12, said body having a diameter between 2 inches and 10 inches inclusive.
 19. The stator of claim 12, said body having an exterior surface, the stator further comprising: means for removably affixing said stator within a shell of the progressive cavity pump. 